Sound Transit's tunnel boring machine arrives at U District station

One of Sound Transit's tunnel boring machines last week bored through the wall of the the U District light-rail station, which is one of four along the agency's planned Northgate Link extension project.

The boring machine milestone marked the completion of the third segment of the twin 3.5-mile tunnels that will serve light-rail trains from Northgate Mall in Seattle to the University of Washington beginning in 2021, Sound Transit officials said in a press release.

Three more tunnel segments remain to reach Husky Stadium.

The machine dug out 200,000 tons of dirt to reach the station, said Sound Transit Chair Dow Constantine.

Sound Transit's video of 'Brenda' reaching the U District light-rail station site.

JCM Northlink LLC is serving as Sound Transit's tunneling contractor for the Northgate Link light-rail extension. "Brenda," the boring machine that reached the U District station last week, launched July 2014 from the Maple Leaf Portal south of Northgate Mall.

The machine will undergo maintenance at the U District station site before continuing south and connecting with the University of Washington Station, which is slated to open with University Link in the first quarter of next year.

A second machine is expected to arrive at the U District site early next year.